(578a) A Novel Semiconductor Nanofiber with Superb Charge Conductivity for Energy and Environmental Applications

A novel nanostructure embedded into a semiconductor nanofiber that results in superb conductivity has been developed. The nanocomposite addresses a key inhibitor to conductivity, with the potential to improve a wide range of applications, from batteries and solar cells, to air purification devices. While semiconductors are widely used, their effectiveness has been limited by the natural process of photo-generated electrons in recombining with ‘holes’. This reduces the moving current of electrons generated by light or external power and, as a consequence, reduces the efficiency of the device.

We have designed a composite nanofiber that essentially provides a dedicated superhighway for electron transport once they are generated, eliminating the problem of electron-hole recombination. We have avoided recombination by inserting a highly conductive nanostructure made of carbon nanotubes and graphene into a titanium dioxide (TiO2) composite nanofiber. The electrons and charges can be transported efficiently in the graphene core as soon as they are generated, prior to recombining with the ‘holes’ in the nanofibre.

We have tested the effectiveness of the nanocomposite in solar cells and air purification photocatalysts. We have embedded the nanocomposite into the TiO2 component of dye-sensitized and perovskite-based solar cells, which are under investigation as alternatives to conventional silicon-based solar cells. The nanocomposite boosted the DSSC’ energy conversion rates 40% to 66%.

TiO2 nanoparticles are the most commonly used photocatalyst material in commercially available air-purifying or disinfection devices. However, TiO2 can only be activated by ultraviolet light, which renders it far less effective indoors. It is also ineffective at converting nitric oxide (NO) into nitrogen dioxide (NO2), at a rate of less than 10%. When our nanostructure was embedded into a photocatalyst, it provided a graphene superhighway for electrons to transport more quickly to generate super-anions to oxidize absorbed pollutants, bacteria and viruses. The graphene core also significantly increased the surface exposed for light absorption and trapping harmful molecules. It also harvested more light energy across all wavelengths. The semiconductor nanofibre converted about 70% of NO to NO2, seven times more than plain TiO2 nanoparticles. We have also tested how well their nanostructure breaks down formaldehyde, a nasty volatile organic compound commonly found in new or renovated buildings and new cars. Our embedded graphene photocatalyst again was able to break down three times more formaldehyde than TiO2 nanoparticles without the added nanostructure. The new nanocomposite has a wide range of other potential applications, such as hydrogen generation by water splitting, biological-chemical sensors with enhanced speed and sensitivity, and lithium batteries with lower impedance and increased storage.

Biography of Wallace Woon-Fong LEUNG

Dr. Wallace W-F Leung received his MS and ScD both from MIT. For the past 40 years, he has worked on chemical engineering. For 18 years, he was with Bird/Baker Hughes as Senior Research Scientist and Director of Process Technologies directing centrifugal separation/filtration. Earlier, he has worked for Gulf Oil and Schlumberger on flow in petroleum reservoirs. For the past 13 years, he is Chair Professor of Innovative Products and Technologies at The Hong Kong Polytechnic University. Besides air filtration, he is also interested in applications of nanofiber technologies in renewable energy (photovoltaics, hydrogen production using water spliting), clean air and water (photocatalysis), and health technologies (wound dressing).

Dr. Leung is a fellow of, respectively, American Institute of Chemical Engineers, American Society of Mechanical Engineers, American Filtration and Separations Society, Hong Kong Institute of Engineers, and Hong Kong Academy of Engineering Sciences. He has 49 US patents and two books to his credit.